Devices that monitor or measure energy, power or the spatial intensity profile of a light beam, such as a laser beam, have in the past been intrusive such that they intrude upon, and interrupt, the beam path in some fashion thereby extracting a portion of the energy power from the beam. In many cases the entire beam must be directed into a beam energy power meter or spatial energy intensity profile camera.
In high volume production manufacturing facilities using high power laser beams for materials processing applications, including laser welding, laser cutting, laser heat treating and laser free forming, laser power is routinely and continuously monitored. However, by intrusively dissecting a main primary laser beam and directing the dissected portion into a power meter, the routine and continuous monitoring results in a portion of the usable laser power being sacrificed. In these facilities the beam spatial intensity profile is only monitored or checked infrequently, and not on a continuous basis, because this procedure requires a costly interruption or stoppage of production of the company's products.
Because the quality of laser processed products is highly dependent on laser beam power and precise beam profile control it is desirable to non-intrusively and continuously monitor laser beam parameters while maintaining an ability to immediately make changes or compensations when the parameters unacceptably fluctuate or change over time. The embodiments of the present invention solve the aforementioned problems by non-intrusively monitoring only the unused small portion of scattered light or laser light that is conventionally lost off the surface of an optical lens or mirror that is typically required to reside in the beam path to accomplish the intended laser process application.
As described below, the patent literature includes numerous examples of light monitoring devices.
U.S. Pat. No. 4,842,404 discloses a system for monitoring the energy power in a light beam resulting in the least amount of intrusion into the light beam as possible. However, even with the system disclosed, a “beam splitter” optic is placed into the primary beam path to reflect a substantial portion of the beam into an orthogonal axis for directing it into an energy power meter while a majority of the primary beam is allowed to pass through.
U.S. Pat. No. 5,523,837 describes an “essentially non-intrusive laser power meter.” However, the invention utilizes a “beam splitter” that is intrusively placed into the beam path splitting off 1% to 5% of the beam which is then directed into a silicon photodiode power meter.
U.S. Pat. No. 4,792,690 discloses a laser beam monitoring device utilizing a transmitting crystal optic intrusively placed into the beam path that produces a color pattern that corresponds to the laser beam intensity distribution profile. U.S. Pat. No. 6,396,062 discloses a laser beam monitor that requires placement of a fluorescent screen into the primary laser beam path such that the screen is monitored by a camera wherein the images captured by the camera may then be displayed on a computer screen.
U.S. Pat. No. 4,745,280 discloses a laser beam profiling apparatus that requires intrusive attenuation of the beam accompanied by a device that scans the attenuated beam across a photo sensor which produces an electric signal proportional to the beam intensity so as to permit adjustment of the oscillation mode of the laser beam to achieve an efficient beam. U.S. Pat. No. 4,764,655 discloses a device to monitor the size of the focused laser beam and to perform a closed loop adjustment through a robot when necessary.
Each of the above-described devices is intended to monitor or measure the power level or beam mode quality of the light beam but each device is intrusive. A possible exception is an expensive custom made diffraction grating mirror, but such mirrors typically extract noticeably usable and excessive quantities of power from the primary beam. The embodiments of the present invention comprise non-intrusive devices which do not extract more energy power from the primary beam than would typically be lost to scatter.